Chapter 2. Epithelial Tissuejcyxy.ahmu.edu.cn/_upload/article/files/7d/9e/e5bb... · Functions: protection (skin epi.), secretion, absorption (intestinal epi.), excretion (skin) and

Chapter 2.

Epithelial Tissue

Li-jie Feng Ph.D.

Email: [email protected]

Department of Histology and Embryology School of Basic Medical Sciences

Anhui medical university

Anhui Medical University

mailto:[email protected]�

• http://www.dartmouth.edu/~anatomy/Histo/ (Dartmouth medical school)

• http://www.meddean.luc.edu/lumen/MedEd/Histo/virtualhistology.htm (Loyola U. Chicago)

• https://histo.life.illinois.edu/histo/atlas/slides.php (U. of IL-U.Ch.)

Learning website


Key points

• General features of epithelium.

• Classification of covering epithelium

• Features of 6 types of covering epithelium

• Epithelial specialisations of free, lateral and basal surfaces, respectively.


Overview

Epithelium is a tissue composed of closely

aggregated cells and very little extracellular matrix.

Epithelium cover body surfaces, line body cavities,

and constitute glands.


1. General features

1) contain more cells and less extracellular groundsubstance

2) Polarity:--free surface: face air or lumen--lateral surface--basal surface: face underlying CT,

3) Have basement membrane4) Avascularity, but innervation:

---no blood vessels---rich in nerve terminals


• Functions: protection (skin epi.), secretion, absorption

(intestinal epi.), excretion (skin) and sensory reception


2. Classification1) Covering epithelium: the epithelium which cover body surface or line the inner surface of body cavities, tubeand sac.2) Glandular epithelium: the epithelium which main function is secretion.3) Sensory epithelium: the epithelium which has specialsensory function.4) germinal epithelium5) myoepithelium


3. Covering epithelium

According to the number of layer and shape of cells

• Simple epi.: simple squamous epi.simple cuboidal epi.simple columnar epi.pseudostratified ciliated columnar epi.

• Stratified epi.: stratified squamous epi.stratified columnar epi.transitional epi.


1) Simple squamous epi.

Structural feature: one layer of flattened cells, cell border are

interdigitate with flattened ellipsoid nucleus

Basementmembrane

flattened ellipsoid nuclei

Cell border

tightly-connected cells


Distribution • mesothelium: the simple squamous

epi. which lines the inner surface of body cavities such as thoracic, pericardial and abdominal cavities.

• endothelium: the simple squamous epi. which lines the inner surface of cardiovascular and lymphatic systems.

• other places: alveoli, parietal layers of renal capsule.

Function: a) transport of materialsb) facilitates movement of viscera

endothelium

mesothelium

Flat-viewtightly-connected cells

Side view

Blood cells

2) Simple cuboidal epi.

Structural feature: one layer of cells, with same height and width ( in side view) and hexagonal outline (in surface view), a spherical centrally-located nucleus

spherical centrally-located nuclei

same height and width


Distribution: the renal tubulethyroid folliclethe some ducts of many glands

Main function: lining, secretion or absorptionkidney collecting tubules

Simple cuboidal epithelium


3) Simple columnar epi.

Structural features: one layer of columnar cells, with basally located ovoid nucleusGoblet cell: scattered, secreting granules-mucinogen granules-mucus

basally located ovoid nucleus goblet cells


Distribution: gastrointestinal tractgall bladderuterusmany glands

Function: secretion and absorption


4) Pseudostratified ciliated columnar epi.

Structural feature: four types of cellscolumnar cell: ciliatedgoblet cellfusiform cellbasal cell: pyramid-shaped

cilia goblet cellfalse appearance


Distribution: inner surface of much of respiratory tract

trachea

bronchi

nasal

Function: Lining, secretary, absorptive function


5)Stratified squamous epi.

Structural features:Basal cells: one layer of cuboidal cellsIntermediate cells: several layers of polygonal – shaped cells Surface cells: more and more flattened

basal cells

intermediate cells

surface cells


Distributon: • non-keratinized: mouth, pharynx, oesophagus, urethra

and vagina• keratinized: the surface of body, make up the skinFunction: protect from mechanical trauma and bacterial

invasion

Nonkeratinized stratified squamous epithelium

Keratinized stratified squamous epithelium


6) Transitional epi.Structural feature: flexible-including the number of layers and shape of cells.In the distended bladder: there are two to three layers of cells. The cells become flattened.In the contracted bladder : there are six to seven layers of cells. The surface cells, facet cells, are very large and cuboidal in shape, covering several deep cells. Distributon: bladder Function: stretching

contracted facet celldistendedfacet cell


4. Epithelial specialisations


1) Specialisations of free surface

Microvilli

Cilia


① Microvilli

A CB

Microvilli are finger-like cytoplasmic projection on the free surface of most epithelial cells.

Function: increase the surface areasDistribution: striated border: intestinal epi.

brush border: proximal renal tubule


② Cilia:

elongated, mobile projections of cell membrane and cytoplasm protruding from free surface


Structure: core: microtubules, 9X2+2, dyneinbasal body: centrioles-connected with microtubules

Function: protection, swing to produce a forward-moving waveDistribution: epithelial cells of respiratory tract

A B

Cilia


2). Specialisations of lateral surfaceThe lateral membranes of many epithelial cells often exhibit several types of membrane modifications---the intercellular junctions.

Tight junction (zonula occludens)

Intermediate junction (zonula adherens)

Desmosome (macula adherens)

Gap junction (communicating junction)


① Tight junction (zonula occludens)

Function: seal the space between cells, barrier

Structure: point-liked fused between adjacent cells, arranged in 2-4 thread-liked structures, form anastomosing network


② Intermediate junction (zonula adherens)

Function: adherens, keep the cell shape, transfer cell contract force

Structure: below the tight junction, a gap of 15-20nm in width with medium electron-density, filament material plaque of electron-dense materials, with attached microfilament-make up of terminal web


③ Desmosome (macula adherens)

Function: firmly connection

Structure: plate or spot-shaped；a gap of 20-30 nm, with low electron-density filaments；form intermediate line；attachment plaque: with attached tonofilament (10nm)-intermediate filament (karatin)


④ Gap junction (communicating junction)

Function: a pathway, allow communication between cells

Structure: the smallest gap of 2-3 nm connexons: bridge like structures, -7~9nm in diameter

-composed of 6-subunits of proteins- connexin-2nm channel: hydrophilic channel


① Basement membrane:Defination: a sheet of amorphous material interposed between

epi. cells and underlying CT.Structure: EM: three layers

--lamina lucida:--basal lamina:--reticular lamina:

Function:support, connection, fixatonsemi-permeable membraneinduce the movement, proliferation

and differentiation of epi. cell

3)Specialization of basal surface

lamina lucida

basal lamina

Reticularlamina


② Plasma membrane infolding (basal longitudinal striation):Defination: the infolding of cell-membrane with many mitochondria at the surface of epi. cellFunction: increase the basal surface areas, facilitate the passage of water and ionsDistribution: mainly in proximal and distal renal tubule.

mitochondria


③ Hemidesmosomesis half of desmosome.

Function:bind the epithelial cells to the subjacent basal lamina


Questions?

1. What are the classification and features of epi.?

2. What differences are there between the microvillus

and cilium?

3. How many kinds of intercellular junctions are there

between epithelial cells?

4. How many kinds of cells does the pseudostratified

columnar epithelium include?


Documents

Chapter 2. Epithelial Tissuejcyxy.ahmu.edu.cn/_upload/article/files/7d/9e/e5bb... · Functions: protection (skin epi.), secretion, absorption (intestinal epi.), excretion (skin) and